Certain abnormalities of either the cardiac muscle or the conductive system of the heart can result in pathologically high heart rates. If the high rate or tachycardia originates in the atrium, it is called a supraventricular tachycardia, which is transmitted to the ventricles, through the atrioventricular node (A-V node) and into the ventricular conduction system. Another source of an abnormal heart rate is a reentry path that is often located within the AV node.
In the two medical conditions cited above, as well as other causes of tachycardia, it is often mandatory to suppress the abnormally high rate. The treatment of choice is suppression by drug therapy. However, in certain instances, such therapy is not successful, and other avenues must be explored. Overdriven suppression in one method of treatment, where one applies cardiac stimulation at a rate above the tachycardia rate. As the abnormally high rate is controlled, the stimulation rate, applied by a cardiac pacer, is reduced to a normal level.
As a last resort, surgical intervention takes place in the form of a thoracotomy, which involves the mapping or location of the abnormal electrical activity, followed by the destruction of the appropriate structure. If the inner surfaces of the ventricles are to be mapped, then not only is a thoracotomy required, but also the patient must be placed on circulatory bypass, with its attendant risks.
It is desirable to achieve selective destruction or ablation of the appropriate structure using catheter techniques rather than major surgery. Various electrode configurations on a catheter have been suggested for use in such procedures. The catheter is introduced into the heart via an appropriate vein. Under fluoroscopic control, the electrodes carried on the catheter are positioned at various places on the heart wall and the detected electrical activity recorded. However, with many catheter designs no means have been available to destroy the site of abnormal activity located in this manner.
Mapping catheters have also been suggested, having an optical fiber which can transmit laser energy, or which carry a heating element, to destroy the pinpointed source of abnormal action.
Also, a catheter has been used which can deliver a powerful electric shock to an aberrant focus, thereby destroying it. In use, once the abnormal focus has been identified, suction may be applied, stabilizing an electrode-bearing catheter tip by drawing cardiac tissue into the lumen of a protruding tubular electrode. Then, the electric (typically D.C.) shock is applied, thereby destroying the focus.
The use of such a catheter has not been without its attendant difficulties. Because of the thinnes of the tubular electrode, coring of the tissue into the electrode has occurred during the process. If this occurs in the A-V node area, a septal defect may occur. Further, because the electrode delivers a D.C. shock, with its attendant high temperature, thermal destruction of both the electrode and the catheter material to which the electrode is bonded can occur. When such catheter damage occurs, foreign material may be left in the cardiovascular system. Also, to continue the process, the physician must then insert another catheter into the heart.
The suction/ablation catheter of this invention provides for the elimination of coring of cardiac tissue, as well as the prevention of electrode and catheter destruction by the heat generated during the electric shock. Thus it is safer to use, and it can be used repeatedly in the same patient, particularly for dealing with multiple sites in a heart causing tachycardia.